which is equivalent to the following minimization problem [1]}, [2]}
\(\inf _{u \in X, b \in Z}L_{GM}(u , b ): = D(u)+ \frac{\mu }{2} \int _{\Omega }\left[ b \frac{|\nabla u |^2}{\lambda } +b -2\sqrt{b }+1 \right]\mathrm {d}\sigma , \quad b \ge 0.\) 
